Method and apparatus for observing transient gyromagnetic resonance

ABSTRACT

Gyromagnetic resonance spectrometers and methods of operating same are disclosed wherein gyromagnetic resonance of a sample of matter is excited and detected at a first electron resonance condition repetitively and abruptly purturbating said sample of matter to produce a train of transient resonance responses after said purturbation is removed. Establishing a second electron resonance condition within the sample. The transient response is detected as a function of the relatively slow changes in the electron resonance condition to obtain an output transient resonance spectrum.

United States Patent 1191 Hyde 1451 Nov. 6, 1973 [5 METHOD AND APPARATUSFOR 3,469,181 9/1969 Staples 324/05 OBSERVING TRANSIENT GYROMAGNETIC3,562,631 2/1971 Lee 324/05 3,588,678 6/1971 Ernst 324/05 RESONANCEJames S. Hyde, Stockholm, Sweden [75] Inventor: Primary ExaminerMichaelJ. Lynch [73 Assignee: Varian Associates, Palo Alto, Calif.AttorneyStanley Z. Cole [22] Filed: May 15, 1972 [21] Appl.' No.:253,667 7 ABSTRACT Related A fi fi Data Gyromagnetic resonancespectrometers and methods [63] Continuation of Ser No 29 916 April 201970 of operating same are disclosed wherein gyromagnetic abandonedresonance of a sample of matter is excited and detected at a firstelectron resonance condition repetitively and 52 us. c1 324/05 R PPurturbating Said Sample "12mm Pmduce 51 1111.0. 00111 27/78 a transientresponses after said P [581 Field or Search 324/05 R 0.5 A Wham isremoved- Establishing 616cm)" 324/05 resonance condition within thesample. The transient response is detected as a function of therelatively slow [56] References Cited changes in the electron resonancecondition to obtain 1 UNITED STATES PATENTS an output transientresonance spectrum.

3,358,222 12/1967 Hyde 324/05 22 Claims, 10 Drawing Figures 7 52 4 2 7 ql? T FLASH SAMPLE MAGNET LAMP J PROBE CONTROL 1 A (0) 6 6/ 8 t1 tats ml3 R RRR A N C E Y RHRRR'ET *1 INTEGRATOR EXCITER & SAMPLE 81 DETECTORSTORAGE 4 15 DISCHARGE MAGNET TRIGGER PULSE SWEEP A PROGRAMMER RQ TPATENTERNNT 6 I973 3,771, 5

GREET1GT4 5 FIG. I Y4 7 '9 FLASH E SAMPLE MAGNET LAMP J PROBE CONTROL TN? A O I R E GON A N G E' ,2 GAONN'E'E 2 EXCITER & SAMPLE& *NTEGRATORRECORDER GETEGTGR STORAGE TNsGNARGE X MAGNET E PULSE A TR'GGERPROGRAMMER s 2 I6 I4 FIG 2 FLASH SAMPLE MAGNET Z LAMP PROBE CONTROL TGYROMAGNETI MuETl- A RESONANCE CHANNEL EXCITER& SAMPLE& 2 DETECTORsToRAGE H7 X PULSE MAGNET REOOR OE R TR'GGER ""PRGGRAMMER SWEEP 443 A AA CIRCUIT A If; W V M JAMES :sOT Y'ET E A FIG. 3 B? 7 2 f-''-- '*A TTMEM FLASH 0N ATTORNEY PAIENIEIIIIIIII BIEITT 3771.054

SHEET 20F 4 A FIG.4

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2| 25 2 l6' l4 MICROWAVE Dl0DE BIMODAL MAGNET GRAPHIC Q 'SWITCH CAVITY[L CONTROL QP 9 fin. 27 4 165 I INTEGIRATOR GYROMAGNETIC 7 1H RESONANCEq QQ 5% 8 TANALYE -,|NTEG RAT0R n 0|scRARGE-- 1 M28 [H 9 I MAGINET i Y-PULSE TRIGGER SWEEP APHIC PROGRAMMER CIRCUIT RECORDER v s. R l4 FIG.7

ORDINARY E.P.R SPECTRUM HORT TRANSIENT 52 0 /\/m a PURE ABSORPTION gOBSERVED 5| v RFROM RADICAL #I 3 LONG TRANSIENT 55 0 7 PURE SORPTION 0TIME G FROM RADICAL 2 56 54 HIGH PASS 0 R 26? F R FIG.8

FROM l 5? R I I A l ..i .i F|G.9

B INVENTOR I 5 JAMES s. HYDE |-LOWPASS AWORNEY METHOD AND APPARATUS FOROBSERVING TRANSIENT GYROMAGNETIC RESONANCE This is a continuation ofapplication Ser. No. 29,916 filed Apr. 20, 1970, now abandoned.

DESCRIPTION OF THE PRIOR ART Heretofore, pulsed electron-electron doubleresonance experiments have been performed wherein one part of anelectron paramagnetic resonance spectrum was irradiated with a pulsedsource of microwave energy while the resulting transient response wasobserved at a certain portion of the spectrum. Such an experiment isdisclosed in Volume 115 of the Physical Review, page 986, appearing in1959; Volume 118 of the Physical Review, page 939, appearing in 1960;and Volume 129 Physical Review, page 2,441 appearing in 1963.

It is also known that an electron spin resonance spectrum of asample'can be obtained by pumping the spectrum with a relatively strongRF pump field to saturate resonance of the spectrum While simultaneouslyprobing the spectrum under analysis with weak RF detector field appliedat a different frequency, such spectrometer and method of operating sameis disclosed in Physical Review, Volume 135, No. la of July, 6, 1964, atpage A247.

SUMMARY OF THE PRESENT INVENTION The principal object of the presentinvention is the provision of improved method and apparatus forobserving transient gyromagnetic resonance.

One feature of the present invention is the provision of exciting anddetecting gyromagnetic resonance of a sample of matter, and whiledetecting such resonance, repetitively and abruptly purturbating andremoving said purturbation on said sample to produce a train oftransient responses in the detected resonance of the sample, changingthe electron resonance condition within the sample with a time rate ofchange slower than the abrupt purturbations, and detecting 'the changesin the transient resonance response as a function of changes in theelectron resonance condition.

Another feature of the present invention is the same as the precedingfeature whereinthe purturbation includes one or more of the followingconditions: irradiation of the sample either in the optical or radiofrequency spectrum, temperature of the sample, electrical currentpassing through the sample, and phase of the RF energy applied to thesample.

Another feature of the present invention is the same as any one or moreof the preceding features wherein the electron resonance condition,which is changed at a relatively slow rate, is a function of thepolarizing magnetic field intensity or the frequency of an alternatingRF field applied to the sample to excite resonance.

ing specification taken in connection with the accompanying drawingswherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagram ofa gyromagnetic resonance spectrometer incorporating features of thepresent invention, 1

FIG. 2 is a schematic block diagram, similar to the block diagram ofFIG. 1, depicting an alternative embodiment of the present invention,

FIG. 3 is a plot of the detected resonance signal as a function of timefor the spectrometer system of FIG. 2,

FIG. 4 is a schematic block diagram of an electron paramagneticresonance spectrometer incorporating features of the present invention,

FIG. 5 is a schematic block diagram depicting an alternativespectrometer embodiment incorporating features of the present invention,

FIG. 6 is a schematic block diagram of further electron paramagneticresonance spectrometer incorporating features of the present invention,

diagram form, depicting a portion of the spectrometer FIG. 7 is a plotof resonance signal amplitude versus time depicting the transient outputsignal obtained in a portion of the spectrometer of FIG. 6,

FIG. 8 is a plot of three output spectra derived from the spectrometerFIG. 6 and depicting different frequency components of the compositetransient resonance responses,

FIG. 9 is a schematic circuit diagram, partly in block of F IG. 6delineated by line 9-9, and

FIG. 10 is a schematic block diagram of an electronparamagneticspectrometer incorporating features of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, thereis shown an'electron paramagnetic resonance spectrometer l incorporatingfeatures of the present invention. The spectrometer 1 includes a sampleprobe structure 2 having a gyromagnetic resonance sample materialdisposed in RF magnetic field exchanging relation with a resonantcircuit for exciting and detecting gyromagnetic resonance of the samplematerial. The resonant circuit comprises a cavity resonator having alight transmissive wall portion for irradiation of the sample by a flashlamp 3. A magnet having pole pieces 4 and 5 produced an intense DCmagnetic field within the sample. Each line in an EPR sample spectrumrepresents an electron resonance condition obtained by establishing theexciting frequency and polarizing field such that gyromagnetic resonanceOCCLII'S.

A gyromagneticresonance exciter and detector is coupled to the resonantcircuits within the probe 2 for exciting and detecting gyromagneticresonance of the sample material. The gyromagnetic resonance exciter anddetector 6 supplies a radio frequency magnetic field to the sample at anangle to the polarizing magnetic field, thefrequency of the radiofrequency magnetic field being such as to produce gyromagnetic resonanceof the gyromagnetic bodies within the sample material for the particularvalue of the polarizing field. The resonance of the sample is detectedin the gyromagnetic resonance exciter and detector and the transientresonance signals are fed by a coupling capacitor 7 to the input ofamultichannel sample and storage unit 8.

In a typical example of the present invention, the gyromagneticresonance bodies are electrons, the radio frequency magnetic field has afrequency on the order of 10 GH, and as an aid in detecting resonance,the magnetic field is modulated at a relatively high frequency, such as100 KI-I to permit synchronous detection of the 100 KH component in theresonance signal.

Alternatively, if the transient response to be investigated issufficiently rapid, magnetic field modulation may be eliminated sincelow frequency noise components of the response distorted by the detectorwill not pass the coupling capacitor.

A pulse programmer 9 produces a train of output pulses which are fed toa trigger 11 which in turn produces atrain of trigger pulses fed to theflash lamp 3 such as an Xenon flash tube, which produces an output trainof purturbating light flashes which are applied to the samplegyromagnetic resonance material within the polarizing magnetic field HIn a typical example, output flashes from lamp 3 have a repetition rateof 10 per second, each flash from the lamp having a duration, of i0microseconds. Each flash from the lamp 3 produces acorrespondingtransient change in the continuously detected resonance ofthe sample material if the sample is light sensitive. Thus, a train oftransient resonance responses is obtained in the output of thegyromagnetic resonance exciter and detector which is coupled to theinput of the multichannel sample and storage 8. Each transient responsein the train of transient responses has a characteristic envelope suchas depicted by curve 12 of the waveform diagram (a). The multichannelsample and storage unit 8 is synchronized with each transient responsevia an input from the pulse programmer 9. The multichannel sample andstorage unit 8 samples each transient response signal 12 at a number oftime displaced intervals indicated at t t t t Each sampled responseamplitude is stored in a separate respective channel of the multichannelstorage .unit 8. After one or more of the transient responses 12 hasbeen sampled and stored in the multichannel sam ple and storage unit,the outputs of the respective channels are fed into the input of anintegrator 13 which integrates the output of each of the channels toobtain a total output which is fed to one input of a recorder 14.

After one or more of the transient responses 12 has been integrated bythe integrator 13, the pulse programmer 9 sends a pulse to theintegrator, thereby discharging same, and also at the same time sends apulse to a magnetic sweep circuit 15 which produces an output to amagnet control unit 16 for changing the magnitude of the polarizingmagnetic field I-I to a new value slightly different from the intensityof the polarizing magnetic field in the sample used to derive the firsttrain of transient responses, thereby changing the electron resonancecondition. At the same time, a sample of the output of the magneticsweep circuit 15 is fed to the recorder 14 for recording the output ofthe integrator 13. The pulse programmer 9 periodically advances themagnetic field intensity until the magnetic field intensity has beenswept in a successive number of discrete steps through the electronresonance condition spectrum of the sample under analysis. The result isa recorded output spectrum of the transients of resonance lines whichare sensitive to light. Other resonance lines in the sample which arenot sensitive to light would be suppressedin the recorded spectrum.

If the multichannel sample and storage unit 8 is set to accumulate theoutput of a number of transient responses before the pulse programmer 9advances the magnetic field; a time average of the output transientresponses is obtained, thereby improving the signal to noise ratio ofthe final output recorded spectrum. One advantage of the spectrometer ofFIG. 1 is that, provided the alternative of no magnetic field modulationis employed, the recorded resonance lines are pure absorption moderesonance and not derivative like" first harmonic output signals of aphase sensitive detector.

As an alternative to sweeping the magnetic field, the output of thepulse programmer 9 may be applied for changing the frequency of theexciting radio frequency magnetic field applied to the sample. Thischanges the electron resonant condition in the same manner as a changein the magnetic field.

As still another alternative to the spectrometer of FIG. 1, the flashlamp 3 need not irradiate the sample material with optical radiation butthe purturbation may be a pulsed microwave source which sharply raisesthe temperature of the sample material due to dielectric heating withinthe sample. As another alternative the flash lamp 3 may be replaced byan electrical discharge device for producing a pulse or step of currentor voltage through the sample material within the probe 2. In each ofthe above alternatives, the transient response in the detected resonanceof the sample material in response to the abrupt purturbation in thetemperature, the current, voltage or the like applied to the sample isdetected and fed to the multichannel sample and storage unit 8 foranalysis as above described. In each of the aforementioned alternatives,the recorded output spectrum, obtained from recorder 14, comprises aspectrum of the transients of resonance line signals which are sensitiveto the resonance affecting purturbation such as light, temperature,phase of the RF, voltage, current, etc.

In another alternative embodiment of the spectrometer of FIG. 1, themultichannel sample and storage unit 8 may be deleted and the output ofthe coupling capacitor 7 merely fed to the input of the integrator 13for integrating the area under curve 12. The pulse programmer 9 woulddischarge the energy of the integrator 13 after integration of eachofthe output transient responses and before advancing to the magneticfield via the magnetic sweep circuit 15.

In another embodiment of the spectrometer of FIG. 1, the multichannelsample and storage unit 8 takes only a selected one sample out of eachtransient resonance response 12, such sampling time may be arbitrarilychosen as any one of the channels of the sample and storage unit 8. Thisrepresentative channel is then employed for sampling each successivetransient resonance response 12 and the sampled output is stored for asuccession of transient resonance responses 12 for a given electronresonance condition. The sampled amplitudes are accumulated in theselected channel to obtain a time average and the accumulated total isread out directly to the recorder 14 without the necessity of integrator13.

' Referring now to FIG. 2, there is shown an alternative spectrometer ofthe present invention. The spectrometer of FIG. 2 is essentially thesame as that of FIG. 1 with the exception that the coupling capacitor 7between the gyromagnetic resonance exciter and detector 6 and the inputto the multichannel sample and storage unit 8 has been deleted such thatan output including the DC resonance is fed to the multichannel storageunit 8 with the transient response superimposed thereon, as shown inFIG. 3. This configuration employs magnetic field modulation and phasesensitive detection. This resonance signal is characterized by a more orless continuous DC resonance signal level with the transient responsesuperimposed thereon, there being a transient resonance responsefollowing each of the pulses of the lamp 3.

The multichannel sample and storage unit 8 is synchronized by the pulseprogrammer 9 in such a manner that'the sampling times for the outputresonance signal, t 2,, t t start slightly before the initiation of thelight flash from lamp 3 and continue for a'time after the transientresponse has returned to the DC level. A number of the transientresponses are sampled and stored in the storage unit 8 such that theresults for the various channels are accumulated in order to obtain atime averaged output having improved signal to noise ratio.Alternatively, each transient output may be sampledand read directly tothe output of the multichannel sample and storage unit 8.

Certain ones of the selected storage channels, corresponding tomeasurements of the resonance signal before initiation of the flash arefed to a Y-axis of a first recorder 14 for recording as a function ofthe magnetic field intensity. Certain others of the channelscorresponding to the transient response are read out to the Y- axis of asecond recorder 14, and a third number of channels corresponding to theperiod following the transient response are read out and fed to theY-axis of a third recorder 14". The result is three separate recordedoutput spectra (a), (b), (c). By comparison of the output spectra (a),(b), and (c) valuable information is obtained concerning the transientresponse of 'the sample material to the pulsed irradiation.

As in the spectrometer of FIG. 1 the flash lamp may be replaced by anyone ofa number of other devices for changing the resonance affectingconditions over the sample in a transient and abrupt manner. Suitablealternatives for the flash lamp 3 include a pulsed microwave source, ora pulse of current or voltage through the sample materiaLAsanalternative to the use ofN number of graphic recorders 14 theresonance data output of the multichannel sample and storage unit 8 maybe stored on a tape recorder or in a computer memory and displayed at alater time on a graphic recorder or printed out in-digital form. 7

Referring now to FIG. 4, there is shown an alternative electronparamagnetic resonance spectrometer incorporating features of thepresent invention. The spectrometer of FIG. 4, is essentially the sameas the spectrometers of FIGS. 1 and 2 with the exception that the flashlamp 3 is replaced by a microwave source 21 and the amplitude ofmicrowave radiation applied to the sample is not altered but instead thephase of the microwave energy is abruptly and repetitively shifted by arelatively large phase angle, as of 180, to produce a train of transientresponses in the resonance of the sample being monitored. Moreparticularly, the microwave source 21 supplies microwave energy at a frequency of f, suitable for excitation of gyromagnetic resonance of asample of material under analysis. A typical spectrum for such a sampleis shown by waveform A. The microwave energy is fed into a three portcirculator 22 having a diode switch placed one quarter of a wave lengthfrom a shorted end of a waveguide attached to one port of the circulatorsuch that when the diode 24 is tired by the output of the trigger 1 l,the microwave energy, instead of being reflected from the shorted end ofarm 23 is reflected from the diode 24, such that now the phase of thewave energy passing out of the circulator to the sample is abruptlyshifted by The probe structure 2 includes a bimodal cavity having thesample material disposed in a region common to two orthogonal modes ofosciallation, one of the modes being the pumping mode and beingconnected to the output of the circulator 22. The other mode of thecavity is coupled to the gyromagnetic resonance exciter and detector 6which excites resonance of the sample material at either the samefrequency of the microwave source, namely f, or at any other frequencyf, suitable for excitation of gyromagnetic resonance within the spectrumof the sample under anaylsis.

The abrupt change in the phase of the pumping energy applied to thesample produces a transient response in the resonance of the line beingdetected and the transient response is coupled via coupling capacitor 7to the multichannel sample and storage unit 8. As in the previousspectrometer embodiments, the sampled transient resonance responses canbe time averaged and integrated or merely time averaged or merelysampled, with the output being fed to the Y-axis of the X-Y recorder 14for recording against the sweep of the electron resonance condition toobtain an output spectrum of the transient responses produced by thetrain of abrupt changes in the phase of the microwave energy employedfor pumping the sample.

Referring now to FIG. 5 there is shown a gyromagnetic resonancespectrometer similar to that of FIG. 4. The apparatus is essentially thesame as that of FIG. 4 with the exception that the phase of themicrowave energy applied for pumping the sample is not changed butrather the amplitude of the microwave energy applied for RF pumping ofthe sample is changed abruptly from a first RF level of sufficientamplitude to produce saturated resonance of a spectral line of thesample to a much lower amplitude, such as 30 db below the saturation RFamplitude to produce a transient resonance response in the excited anddetected gyromagnetic resonance of the sample.

Gyromagnetic resonance exciter and detector 6 excites resonance of aline of the resonance sample, namely f The resonant sample ispurturbated by pulsing the pump power which is of radiofrequency f, andthe train of transient responses produced in the detected resonance iscoupled via coupling capacitor 7 to the input of a single channel samplestorage unit 8. The microwave energy at f from microwave source 21 ispulsed to the lower level by means of diode switch 25 in response to theoutput of trigger 11.

Each transient response, indicated by curve 12 of waveform (b), issampled at some predetermined point, such as point t,, which is selectedby means of a pulse derived from pulse programmer 9 and delayed by asuitable delay time I, in time delay 20 corresponding to the desiredsampling time 2,, following initiation of each transient response. Aplurality of successive transient responses are sampled at the samepoint and the sampled amplitude is accumulated in the single channelsample and storage unit 8. The accumulated total, which corresponds to atime average of the transient resonance response is fed to the Y-axis ofthe X-Y recorder 14 for recording as a function of the differencebetween the frequency of the pumping source and the resonance excitingand detecting frequency. Either the detecting frequency or,alternatively, the frequency of the pumping source is swept inaccordance with the output of the pulse programmer 9. More particularly,sweep circuit 15' changes the tuning of the receiver mode cavity or,alternatively, the pumping mode cavity in the bimodal cavity portion ofthe probe 2. An electro-mechanical frequency control 25 also causes themicrowave source 6 or, alternatively, 21 to shift frequency to track thetuning of the bimodal cavity such that the frequencyf, of the microwavesource 21 or, alternatively, the frequency f of the gyromagneticresonance exciter and detector 6 shifts across the spectrum of thesample under analysis.

The result is an output spectrum of improved resolution as compared tothat obtained from a conventional electron spin spectrometer. Thespectrum is a pure absorption spectrum due to the transient nature ofthe resonance signals being recorded. All the reasons for thesubstantial improvement in resolution of the output spectrum are notfully understood. In a typical example, the abrupt change in the RFlevel of the microwave source as fed to the bimodal cavity for pumpingthe sample, shifts from the high intensity saturation level to thenon-saturation low intensity level in approximately I nanoseconds, asbefore, the repetition rate for the abrupt change in RF level isapproximately l0 per second. Upon" the termination of each transientoutput signal the RF level is returned via pulse programmer 9 andtrigger 11 to the high intensity level and the RF level remains at thehigh intensity level for sufficiently long time for saturation of thesample to reach equilibrium. Typically this is on the order of I00microseconds.

In an alternative embodiment of the purturbation spectrometer of FIG. 5,the frequency f, of the pumping microwave source is approximately thesame as or, alternatively, coherent with or, alternatively, differentfrom the frequency f, of the gyromagnetic resonance exciter and detector6 and the applied polarizing magnetic field is swept by the pulseprogrammer. The resulting transient response is obtained as previouslyand displayed on the graphic recorder 14 as a function of the polarizingmagnetic field.

Referring now to FIG. 6 there is shown an alternative gyromagneticresonance spectrometer incorporating features of the present invention.The spectrometer of FIG. 6 is substantially the same as that of FIG. 4with the exception that the intensity of the microwave source is pulsed,as previously disclosed spectrometer of FIG. 5. The resultant train oftransient output resonance signals are fed via coupling capacitor 7 tothe input of a transient analyzer 26 which separates transients havingdifferent time constants. The separated output transient components fromtransient analyzer 26 are fed to separate integrators 27 and 28 forintegrating the separated transient components. The integrated outputsare fed to separate recorders l4 and 14 for recording separately theseparated transient signals. After the analysis of each transient outputsignal, the pulse programmer 9 pulses the magnetic sweep current tochange the electron resonance condition to observe the transientresonance of a different portion of the spectrum of the sample underanalysis. A sample of the sweep circuit output is fed to the X axis ofthe respective recorders l4 and 14' to obtain seprate output spectra asshown by spectra 2 and 3 of FIG. 8. The conventional ordinary electronspin resonance spectrum is shown by spectrum 1 of FIG. 8.

Referring now to FIGS. 7 and 9 the transient analyzer 26 will be morefully disclosed. Each transient output from the output of gyromagneticresonance exciter and detector 6 may comprise a signal having atransient envelope of decaying amplitude as shown by curve 31 of FIG. 7.Curve 31 represents a composite transient signal, such as that producedby super-position of a short transient signal 32 and a long transientsignal 33. The transient analyzer 26 comprises a parallel connection ofa high pass filter 34 and a low pass filter 35. High pass filtercomprises a series capacitor 36 and shunt resistor 37, whereas the lowpass filter 35 comprises series inductance 38 and shunt resistor 39.High pass filter 34 separates the short transient component from thecomposite transient resonance signal 31 and feeds the short transient tothe first integrator 27. The low pass filter 35 separates the longtransient output signal 33 from the composite resonance signal 31 andfeeds long transient component to the second integrator 28.

As an alternative to analyzer 26, the composite transient signal isdecomposed into the sum of two or more transient exponential functionsin a digital computer. The separated exponentialfunctions may then eachbe integrated independently in the computer by digital techniques andthe output converted to analog form and recorded on an X-Y recorder toobtain the output spectra 2 and 3 of FIG. 8. The spectrometer of FIG. 6is especially useful for separating the spectra of two gyromagneticgroups having overlying spectrums. For example, electrons in theresonance sample may be related to two radical systems having overlyingresonance spectra. The spectra are readily separated according to theirtime constants.

Referring now to FIG. 10 there is shown an alternative spectrometerembodiment of the present invention. The spectrometer of FIG. 10 isessentially the same as that of FIG. 6 with the exception that theoutput of capacitor 7 is fed to the input of a multichannel sample andstorage 8 which samples each transient resonance response, 12 asindicated in waveform (a), at a number of time displaced sampling pointswith each sampling point corresponding to a specific channel of thesample and storage 8. Successive transient resonance responses for agiven electron resonance condition, i.e., magnetic field intensity, areaccumulated in the multichannel sample and storage 8 for time averagingto improve the signal to noise ratio. Periodically the output of themultichannel sample and storage unit 8 is fed to the input ofa timeconstant calculator 41, such as a digital computer, which measures theresponse in the first channel, that response being A, and utilizes thisvalue of A to calculate a value B which is He A.

The computer then compares the calculated value B with the measuredvalues in the various channels to arrive at the time constant T, i.e.,the time at which the signal amplitude has decayed to the value of B.The computer then generates a voltage proportional to T and this timeconstant T is recorded on the Y-axisof recorder 14 as a function of themagnetic field intensity derived from the output of magnetic sweepcircuit 15 to obtain an output spectrum of the sample under analysis. Inthe spectrum, the separate line signals have amplitudes in variableaccordance with the time constants of the various lines.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A method for obtaining a display of changes in purturbation inducedtransients of electron cyromagnetic resonance as a function of electronresonance condition, the steps comprising:

a. continuously exciting and detecting electron gyromagnetic resonanceof a sample of matter at a first electron resonance condition;

b. applying an abrupt purturbation to said sample of matter andcommencing periodic sampling and storage of electron gyromagneticresonance signal at predetermined intervals;

c. discontinuing application of said abrupt purturbation to said samplewhile continuing said periodic sampling and storage of said electrongyromagnetic resonance signal;

d. establishing a second electron resonance condition and continuouslyexciting and detecting electron gyromagnetic resonance of said sample ofmatter at i said second electron resonance condition;

e. repeat steps (b) repeat step (c) t compare the detected signals ofsteps (b) and respectively with the detected signals of steps (e) and(f) and I h. display the comparison determined in step (g) as a functionof electron resonance condition.

2. The method of claim 1 wherein steps (b) and (c) are repeated aplurality of times for each electron resonance condition in order toobtain signal-to-noise improvement by time-averaging.

3. The method of claim 1 wherein the abrupt purturbation of step (b) isan induced temperature jump.

4. The method of claim 2 wherein the abrupt purturbation of step,(b) isan induced temperature jump.

5. The method of claim 1 wherein the abrupt purturbation of step (b) isradiation at optical wavelengths.

6. The method of claim 2 wherein the abrupt purturbation of step (b) isradiation at optical wavelengths.

7. The method of claim 1 wherein the abrupt purturbation of step (b) isa step in the phase of a microwave pumping source, said microwave sourcebeing at the frequency associated with the electron resonance condition.

8. The method of claim 2 wherein the abrupt purturbation of step (b) isa step in the phase of a microwave pumping source, said microwavepumping source being at the frequency associated with the electronresonance condition.

9. The method of claim l'wherein the abrupt purturbation of step (b) isa step in the amplitude of a microwave pumping source, said microwavepumping source being at the frequency associated with the electronresonance condition.

10. The method of claim 2 wherein the abrupt purturbation of step (b) isa step in the amplitude of a microwave pumping source, said microwavepumping source being at a frequency associated with the electronresonance condition.

11. The method of claim 1 wherein the abrupt purturbation of step (b) isa step in the amplitude of a microwave pumping source, said microwavepumping source being at a frequency different from the frequencyassociated with said electron resonance condition.

12. The method of claim 2 wherein the abrupt purturbation of step (b) isa step in the amplitude of a microwave pumping source, said microwavepumping source being at a frequency different from the frequencyassociated with said electron resonance condition.

13. In apparatus for observing electron paramagnetic resonance includinga means for holding a sample of matter under test in a polarizingmagnetic field and a means for applying an RF magnetic field at afrequency to excite an electron resonance condition in said, sample andto detect gyromagnetic resonance of said sample, the improvementcomprising means to periodically purturbate said sample;

means to sample and store said: detected gyromagnetic resonance signalsfollowing the discontinuance of said purburbation;

means to step through differing values of electron resonance conditionof said sample responsive to each cycle of said programmer; programmermeans for synchronizing said purturba tion of said sample and saidsampling and storage of said detected gyromagnetic resonance sig nal andsaid stepping of said electron resonance condition;

means to compare the stored gyromagnetic resonance signals for each saidstep of said electron resonance condition; and

means for displaying said comparison of said detected gyromagneticresonance signals as a function of electron resonance condition. 14. Theapparatus of claim1 13 wherein the means to abruptly purturbate is aflash lamp having radiation in the visible wavelengths. v

15. The apparatus of claim 13 wherein the means to abruptly purturbateis a heater.

16. The apparatus of claim 14 wherein the means to. abruptly purturbateis a microwave pumping source in cluding means to phase switch energyfrom saidsource which impinges upon said sample.

-17. The apparatus of claim 14 wherein the means to abruptly purturbateis a microwave pumping source including means to amplitude step energyfrom said source which impinges upon said sample.

18. Apparatus for observing purturbation-induced transients in theelectron gyromagnetic resonance of a sample of matter comprising,

programming means; means for continuously exciting electron gyromagneticresonance of said sample of matter at selected electron resonanceconditions; said electron resonance conditions being responsive to saidprogramming means;

means for abruptly and, periodically purturbating said sample and fordiscontinuing said purturbations responsive to said programmer means;

means for detecting saidlgyromagnetic resonance signal at apredetermined time interval after discontinuance of said purturbation,said detected signal the amplitude of said detected gyromagneticresonance signal.

21. The apparatus of claim 20 wherein means for comparison furtherincludes a time constant calculator and wherein said display meansincludes means for displaying said time constants as a function ofelectron resonance condition.

22. The apparatus of claim 18 wherein said means for comparing includesmeans for periodic sample and storage of the amplitudes of said detectedgyromagnetic resonance signal to time-average a plurality of detectedtransient signals for each value of electron resonance condition.

1. A method for obtaining a display of changes in purturbation inducedtransients of electron cyromagnetic resonance as a function of electronresonance condition, the steps comprising: a. continuously exciting anddetecting electron gyromagnetic resonance of a sample of matter at afirst electron resonance condition; b. applying an abrupt purturbationto said sample of matter and commencing periodic sampling and storage ofelectron gyromagnetic resonance signal at predetermined intervals; c.discontinuing application of said abrupt purturbation to said samplewhile continuing said periodic sampling and storage of said electrongyromagnetic resonance signal; d. establishing a second electronresonance condition and continuously exciting and detecting electrongyromagnetic resonance of said sample of matter at said second electronresonance condition; e. repeat steps (b) f. repeat step (c) g. comparethe detected signals of steps (b) and (c) respectively with the detectedsignals of steps (e) and (f) and h. display the comparison determined instep (g) as a function of electron resonance condition.
 2. The method ofclaim 1 wherein steps (b) and (c) are repeated a plurality of times foreach electron resonance condition in order to obtain signal-to-noiseimprovement by time-averaging.
 3. The method of claim 1 wherein theabrupt purturbation of step (b) is an induced temperature jump.
 4. Themethod of claim 2 wherein the abrupt purturbation of step (b) is aninduced temperature jump.
 5. The method of claim 1 wherein the abruptpurturbation of step (b) is radiation at optical wavelengths.
 6. Themethod of claim 2 wherein the abrupt purturbation of step (b) isradiation at optical wavelengths.
 7. The method of claim 1 wherein theabrupt purturbation of step (b) is a step in the phase of a microwavepumping source, said microwave source being at the frequency associatedwith the electron resonance condition.
 8. The method of claim 2 whereinthe abrupt purturbation of step (b) is a step in the phase of amicrowave pumping source, said microwave pumping source being at thefrequency associated with the electron resonance condition.
 9. Themethod of claim 1 wherein the abrupt purturbation of step (b) is a stepin the amplitude of a microwave pumping source, said microwave pumpingsource being at the frequency associated with the electron resonancecondition.
 10. The method of claim 2 wherein the abrupt purturbation ofstep (b) is a step in the amplitude of a microwave pumping source, saidmicrowave pumping source being at a frequency associated with theelectron resonance condition.
 11. The method of claim 1 wherein theabrupt purturbation of step (b) is a step in the amplitude of amicrowave pumping source, said microwave pumping source being at afrequency different from the frequency associated with said electronresonance condition.
 12. The method of claim 2 wherein the abruptpurturbation of step (b) is a step in the amplitude of a microwavepumping source, said microwave pumping source being at a frequencydifferent from the frequency associated with said electron resonancecondition.
 13. In apparatus for observing electron paramagneticresonance including a means for holding a sample of matter under test ina polarizing magnetic field and a means for applying an RF magneticfield at a frequency to excite an electron resonance condition in saidsample and to detect gyromagnetic resonance of said sample, theimprovement comprising means to periodically purturbate said sample;means to sample and store said detected gyromagnetic resonance signalsfollowing the discontinuance of said purburbation; means to step throughdiffering values of electron resonance condition of said sampleresponsive to each cycle of said programmer; programmer means forsynchronizing said purturbation of said sample and said sampling andstorage of said detected gyromagnetic resonance signal and said steppingof said electron resonance condition; means to compare the storedgyromagnetic resonance signals for each said step of said electronresonance condition; and means for displaying said comparison of saiddetected gyromagnetic resonance signals as a function of electronresonance condition.
 14. The apparatus of claim 13 wherein the means toabruptly purturbate is a flash lamp having radiation in the visiblewavelengths.
 15. The apparatus of claim 13 wherein the means to abruptlypurturbate is a heater.
 16. The apparatus of claim 14 wherein the meansto abruptly purturbate is a microwave pumping source including means tophase switch energy from said source which impinges upon said sample.17. The apparatus of claim 14 wherein the means to abruptly purturbateis a microwave pumping source including means to amplitude step energyfrom said source which impinges upon said sample.
 18. Apparatus forobserving purturbation-induced transients in the electron gyromagneticresonance of a sample of matter comprising, programming means; means forcontinuously exciting electron gyromagnetic resonance of said sample ofmatter at selected electron resonance conditions; said electronresonance conditions being responsive to said programming means; meansfor abruptly and periodically purturbating said sample and fordiscontinuing said purturbations responsive to said programmer means;means for detecting said gyromagnetic resonance signal at apredetermined time interval after discontinuance of said purturbation,said detected signal being said transient in the electron gyromagneticresonance; means for comparing said detected transient gyromagneticresonance signal at a first selected electron resonance condition to acorresponding detected transient gyromagnetic resonance signal at asecond selected electron resonance condition, and means to display saidcomparison of corresponding detected signals.
 19. The apparatus of claim18 wherein said means for comparing includes means for separating eachsaid detected transient into its component frequencies.
 20. Theapparatus of claim 18 wherein said means for comparing includes meansfor sample and storage of the amplitude of said detected gyromagneticresonance signal.
 21. The apparatus of claim 20 wherein means forcomparison further includes a time constant calculator and wherein saiddisplay means includes means for displaying said time constants as afunctIon of electron resonance condition.
 22. The apparatus of claim 18wherein said means for comparing includes means for periodic sample andstorage of the amplitudes of said detected gyromagnetic resonance signalto time-average a plurality of detected transient signals for each valueof electron resonance condition.